Solid-state imaging device

ABSTRACT

A solid-state imaging-device includes a base, frame-shaped ribs provided on the base and forming an internal space, a plurality of wiring members for electrically leading the internal space of a housing formed by the base and the ribs to an external portion, an imaging element fixed to the base inside the internal space, a transparent plate fixed to an upper surface of the ribs, and connecting members electrically connecting electrodes of the imaging element to the wiring members, wherein a plurality of protrusions are provided in a region of the base that faces the imaging element, and the imaging element is fixed by adhesive to the base while being supported by the protrusions. The protrusions enable the imaging element to avoid distortion caused by following the surface of the base, thereby suppressing the effect on electrical properties of the imaging element.

FIELD OF THE INVENTION

The present invention relates to solid-state imaging devices in which animaging element, such as a CCD or the like, is mounted in a housing.

BACKGROUND OF THE INVENTION

Solid-state imaging devices, which are widely used for video cameras andstill cameras or the like, are provided in the form of a package, inwhich an imaging element, such as a CCD or the like, is mounted on abase made of an insulating material, with the photo-detecting regionbeing covered by a transparent plate. In order to make the device morecompact, the imaging element is mounted on the base as a bare chip. FIG.9 shows the solid-state imaging device disclosed in JP 2001-77277, whichis a conventional example of such a solid-state imaging device.

In FIG. 9, numeral 41 denotes a housing, which is made of a base 41 aand frame-shaped ribs 41 b formed in one piece by resin molding. Aninternal space 42 is formed on the upper side of the housing 41. A diepad 43 positioned at the center of the base 41 a and leads 44 positionedbelow the ribs 41 b are embedded in the housing 41. An imaging elementchip 45 disposed at the center of the internal space 42 is fixed to theupper side of the die pad 43. The leads 44 include internal terminalportions 44 a that are exposed to the internal space 42 at the upperside of the base 41 a on the inner side of the ribs 41 b and externalterminal portions 44 b that are exposed at the bottom side of the base41 a below the ribs 41 b. The internal terminal portions 44 a and thebonding pads of the imaging element chip 45 are connected by bondingwires 46 made of metal. A transparent sealing glass plate 47 is fixed tothe upper surface of the ribs 41 b, thus forming a package forprotection of the imaging element chip 45.

This solid-state imaging device is mounted on a circuit board with thesealing glass plate 47 facing upward, as shown in FIG. 9, and theexternal terminal portions 44 b are used to connect it to the electrodeson the circuit board. Although not shown in the drawings, a lens barrelincorporating an imaging optical system is mounted on top of the sealingglass plate 47 so that a relative position with respect to thephoto-detecting region formed in the imaging element chip 45 is adjustedwith a predetermined precision. During the imaging operation, objectlight that has passed through the imaging optical system incorporated inthe lens barrel is focused on the photo-detecting region andphotoelectrically converted.

Since a solid-state imaging device with such a configuration isconnected at the external terminal portions 44 b exposed from the bottomsurface of the housing to electrodes on the circuit board, the heightand the occupied surface area of the package are smaller than inconfigurations using a connecting structure with outer leads bentdownward from the sides of the housing, thus making it suitable forhigh-density packaging.

In the configuration of the above-described conventional solid-stateimaging device, it is necessary that the base 41 a of the housing 41 hasa sufficient degree of flatness. When, as conventionally, the imagingelement chip 45 is fixed to the surface of the base 41 a with adhesive,and the adhesive hardens, a force is caused that tends to make theimaging element chip 45 follow the surface of the base 41 a. Thus, ifthe degree of flatness of the base 41 a is not favorable, warping andinternal stress are generated in the imaging element chip 45, and theelectrical properties and the like of the imaging element chip 45 areadversely affected.

However, when the base 41 a is molded, it is difficult to avoid acertain degree of twisting or warping of the cross-directional shape,and the degree of flatness is less than desired.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a solid-stateimaging device in which, even if the imaging element is fixed to a basewith unfavorable flatness, generation of distortions caused by theimaging element following the surface of the base can be avoided, andthe effect on electrical properties of the imaging element caused by thedistortions can be suppressed.

The solid-state imaging device of the present invention comprises abase, frame-shaped ribs provided on the base and forming an internalspace, a plurality of wiring members for electrically leading theinternal space of a housing formed by the base and the ribs to anexternal portion, an imaging element fixed to the base inside theinternal space, a transparent plate fixed to an upper surface of theribs, and connecting members electrically connecting electrodes of theimaging element to the wiring members. A plurality of protrusions areprovided in a region of the base that faces the imaging element, and theimaging element is fixed by adhesive to the base while being supportedby the protrusions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing the configuration of asolid-state imaging device in accordance with an embodiment of thepresent invention.

FIG. 2 is a bottom view of the solid-state imaging device of FIG. 1.

FIG. 3 is a lateral view of the solid-state imaging device of FIG. 1.

FIG. 4 is a top view of the solid-state imaging device in FIG. 1 withouta transparent plate.

FIGS. 5A to 5F are cross-sectional views illustrating a method formanufacturing the solid-state imaging device in FIG. 1.

FIG. 6 is a top view of the lead frame which is used in thismanufacturing method.

FIG. 7 is a top view of the molded resin product with the lead frameembedded in this manufacturing method.

FIGS. 8A to 8C are a cross-sectional view showing the resin molding stepof this manufacturing method in more detail.

FIG. 9 is a cross-sectional view of a conventional solid-state imagingdevice.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the configuration of the solid-state imaging device according to thepresent invention, a plurality of protrusions are provided in a regionin which an imaging element is mounted to the upper side of base whichforms a housing, and the imaging element is fixed by an adhesive to thebase while being supported by the protrusions. Consequently, the effectof the imaging element following the surface of the base is suppressed.Thus, even if the imaging element is fixed to a surface of a base whichdoes not have a favorable degree of flatness, adverse effects onelectrical properties caused by distortions is lessened.

In the configuration described above, it is preferable that the numberof protrusions is not less than 3 and not greater than 5. Further, it isalso preferable that the protrusions are substantially hemispherical.The configuration of the present invention is particularly effectivewith a configuration in which the base and the ribs are molded as onepiece with a resin with the wire members embedded.

An embodiment of a solid-state imaging device according to the presentinvention is explained in further detail below with reference to thedrawings. FIG. 1 is a cross-sectional view, FIG. 2 is a bottom view, andFIG. 3 is a lateral view of the solid-state imaging device.

Numeral 1 denotes a housing made of a plastic resin, such as epoxyresin, having ribs 3 arranged as a rectangular frame on a planar base 2and fabricated by molding in one piece. An imaging element 5 is fixed byan adhesive 6 on a base 2 facing an internal space 4 of the housing 1. Atransparent plate 7 made of glass, for example, is fixed with anadhesive 8 to the upper surface of the ribs 3, thus sealing the internalspace 4 of the housing 1 and forming a package.

A plurality of hemispherical protrusions 2 a are provided inside theregion at the upper surface of the base 2 that faces the imaging element5. Thus, the imaging element 5 is fixed by the adhesive 6 to the base 2while being supported by the hemispherical protrusions 2 a. Because ofthis, the imaging element 5 is substantially supported at points, anddoes not follow the surface of the base 2. As a result, the generationof distortions of the imaging element 5 caused by an unevenness of thebase is suppressed. In practice, it is preferable that the number ofhemispherical protrusions 2 a is not less than 3 and not more than 5. Itis preferable that the shape of the protrusions is substantiallyhemispherical, but other shapes are also applicable.

A plurality of metal lead pieces 9 are embedded in the housing 1 byinsert molding. The metal lead pieces 9 are members for providingelectrical leads from the internal space 4 of the housing 1 to theoutside, and include an internal terminal portion 9 a exposed at thesurface of the base 2 on the side of the internal space 4, an externalterminal portion 9 b exposed at a position corresponding to the internalterminal portion 9 a at the rear surface of the base 2, and a lateralelectrode portion 9 c exposed at the outer lateral surface of the base2. The pad electrodes 5 a of the imaging element 5 and the internalterminal portions 9 a of the metal lead pieces 9 are connected by thinmetal wires 10. The thickness of the overall package is set to not morethan 2.0 mm, for example. FIG. 4 is a top view of the planar shape ofthe solid-state imaging device in FIG. 1 without the transparent plate7.

As shown in FIG. 1, the rear side of the metal lead pieces 9 functionsas the external terminal portions 9 b, which correspond to the positionsof the internal terminal portions 9 a. Furthermore, at these portionsthe metal lead pieces 9 have substantially the same thickness as thebase 2. Those portions of the metal lead pieces 9 that are located belowthe ribs 3 are formed thin by half-etching, and their bottom surface iscovered by resin.

As shown in FIGS. 1 and 3, the outer lateral surface of the housing 1,that is to say the outer peripheral surface of the ribs 3, forms aplanar surface that is substantially perpendicular to the surface of thebase 2. Moreover, the end surface of the transparent plate 7 and thesurface of the lateral electrode portions 9 c are substantially flushwith the outer lateral surface of the housing 1. Such a flush shape canbe formed with a favorable flatness by cutting the ribs 3 and thetransparent plate 7 together during the manufacturing process.

A method for manufacturing a solid-state imaging devices configured asabove is explained with reference to FIGS. 5A to 5F, FIG. 6 and FIG. 7.

First, as shown in FIG. 5A, a lead frame 21 is prepared. The lead frame21 is composed of a plurality of lead portions 22 to be used for formingthe metal lead pieces 9 shown in FIG. 1, which are linked as shown inthe top view in FIG. 6. The thickness of the lead portions 22 at thepositions corresponding to the internal terminals 9 a is adjusted to besubstantially the same as the thickness of the base 2. The lead portions22 have recessed portions 23 formed in their bottom surface byhalf-etching, and the shape of the metal lead pieces 9 shown in FIG. 1is attained by cutting at this portion in a later process step.

Next, the lead frame 21 is embedded, as shown in FIG. 5B, and molded inone piece with a resin, thus fabricating together a plurality ofhousings 26 made of a base 24 and rib forming members 25. A plurality(the drawing shows 4 protrusions inside each housing) of thehemispherical protrusions 24 a are formed on the upper surface of thebase 24. FIG. 7 shows the planar shape after molding. The embedding isperformed such that the upper and lower surfaces of the lead portions 22are exposed at the upper and lower surface of the bases 24, forming theinternal terminal portions 9 a and the external terminal portions 9 b,respectively. The rib forming members 25 are formed such that those foradjacent housings 26 are joined into one piece.

Next, as shown in FIG. 5C, the adhesive 6 is applied to the region ofthe housings 26 where the hemispherical protrusions 24 a are formed andthe imaging elements 5 are to be mounted. Thus, the imaging elements 5are mounted such that they are supported on the hemisphericalprotrusions 24 a and fixed by the adhesive 26. Furthermore, the padelectrodes 5 a of the imaging element 5 and the internal terminalelectrodes 9 a are connected by the thin metal wires 10.

Next, as shown in FIG. 5D, an adhesive 28 is applied to the uppersurface of the rib forming members 25, and a transparent plate 27 isplaced thereon and fixed.

Then, as shown in FIG. 5E, the transparent plate 27, the rib formingmembers 25, the lead portions 22 and the base 24 are cut with a dicingblade 29, and separated into pieces forming individual solid-stateimaging devices, as shown in FIG. 5F. As shown in FIG. 5E, the cuttingis performed in a direction perpendicular to the base 24, such that thewidth of the rib forming members 25 in the planar shape is cut in half.As a result, the transparent plate 27, rib forming members 25, leadportions 22 and bases 24, which are thus cut, form a transparent plate7, metal lead pieces 9 and housing 1 made of a base 2 and ribs 3 forconstituting one solid-state imaging device. Moreover, the lateralelectrode portions 9 c of the metal lead pieces 9 are exposed.

According to this manufacturing method, the width of the one rib formingmember 25 in which the two ribs for adjacent housing-equivalent portions26 have been formed as one piece can be set to a smaller width than wheneach of the rib forming members 25 is molded individually. Consequently,when this one rib forming member 25 is cut in half as shown in FIG. 5E,the width of the ribs 3 of each individual solid-state imaging device asshown in FIG. 5F becomes smaller than when each of the rib formingmembers 25 is formed individually, and the surface area of thesolid-state imaging device can be reduced accordingly.

Moreover, when cutting the rib forming members 25 into two pieces in thewidth direction, the cutting plane is perpendicular to the base 24, andthe transparent plate 27, the rib forming members 25 and the leadportions 22 are cut together with the same dicing blade 29. Thereforethe lateral face of the package formed by the end face of thetransparent plate 27, the lateral face of the housing 1 and the end faceof the metal lead pieces 9, is substantially flush, so that a favorableflatness can be achieved. Consequently, when mounting a lens barrelaccommodating the optical system above the imaging device, positioningof the optical system with respect to the photo-detecting portion of theimaging element 5 can be performed with high precision utilizing thelateral face of the package.

Referring to FIG. 8, the following is a more specific explanation of theprocess step for molding the housing with a resin, as shown in FIG. 5Bof the above-described manufacturing process.

First, as shown in FIG. 8A, a lead frame is arranged between the upperdie 30 and the lower die 31, and the upper and lower surfaces of thelead portions 22 are clamped by the upper die 30 and the lower die 31.The upper surface of the lower die 31 is flat, but a recessed portion 32is formed at the lower surface of the upper die 30. By interposing thelead portions 22, the empty portion 33 formed between the upper die 30and the lower die 31, the empty portion of the recessed portion 32 ofthe upper die 30, and the empty portion of the recessed portion 23 ofthe lead portions 22 form the cavities for the resin molding.Hemispherical indentations 30 a are formed on the surface of the uppermold facing the empty portion 33 for molding the base 24, at a position(see FIG. 5B) corresponding to the hemispherical protrusions 24 a on thebase 24.

Next, as shown in FIG. 8B, a resin is filled into the cavity, and thebase 24 and the rib forming members 25 are molded. Hemisphericalprotrusions 24 a are formed at the upper surface of the base 24. Afterthat, the dies are opened as shown in FIG. 8C, and a molded product oflinked housings as shown in FIG. 5B is retrieved.

According to this molding step, it is possible to form easily thehemispherical protrusions 24 a without the addition of steps other thanusual molding for forming the housing, and with only minor alterationsto the upper die 30.

It should be noted that in this molding step, the upper and lowersurfaces of the lead portions 22 are clamped by the upper die 30 and thelower die 31, ensuring that the die surfaces and the upper and lowersurfaces of the lead portions 22 are consistently in close contact.Moreover, the border between the upper die 30 and the recessed portion32 is located on the upper surface of the lead portions 22. As a result,the creation of resin burrs caused by the molding can be effectivelysuppressed.

Moreover, if a resin sheet for the prevention of resin flash burrs canbe arranged between the dies and the lead frame 21 when resin moldingthe housing, then the creation of burrs can be suppressed even moreeffectively,

The invention may be embodied in other forms without departing from thespirit or essential characteristics thereof. The embodiments disclosedin this application are to be considered in all respects as illustrativeand not limiting. The scope of the invention is indicated by theappended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are intended to be embraced therein.

1. A solid-state imaging device, comprising: a base formed with a resin; frame-shaped ribs provided on the base; a plurality of wiring members embedded in the base so as to extend from an internal space of a housing formed by the base and the ribs to an external portion; an imaging element fixed to the base inside the internal space; a transparent plate fixed to an upper surface of the ribs; and connecting members electrically connecting electrodes of the imaging element to the wiring members; wherein a plurality of protrusions are provided on the base, and the imaging element is fixed by an adhesive to the base while being supported by the protrusions, each of the wiring members has a thin portion and a thick portion, the thin portion is located below the rib so as to be recessed from a lower surface of the thick portion, a top surface of the thick portion is connected electrically to the connecting member, a lower surface of the thick portion is exposed from the resin of the base, and a lower surface of the thin portion is covered with the resin of the base.
 2. The solid-state imaging device according to claim 1, wherein the number of protrusions is not less than
 3. 3. The solid-state imaging device according to claim 1, wherein the protrusions are substantially hemispherical.
 4. The solid-state imaging device according to claim 1, wherein the base and the ribs are molded as one piece with a resin with the wiring members embedded.
 5. The solid-state imaging device according to claim 4, wherein the protrusions and the base are formed as one piece with a resin.
 6. The solid-state imaging device of claim 1, wherein the number of protrusions is not greater than
 5. 7. The solid-state imaging device according to claim 1, wherein the protrusions are made of resin.
 8. The solid-state imaging device according to claim 1, wherein the protrusions are formed in a step of forming the base.
 9. The solid-state imaging device according to claim 1, wherein the plurality of wiring members comprise a plurality of metal lead pieces.
 10. The solid-state imaging device according to claim 1, wherein a thickness at the thick portion of the wiring member is substantially the same as a thickness of the base.
 11. The solid-state imaging device according to claim 1, wherein an outer lateral surface of the housing is substantially flush with end faces of the wiring members.
 12. The solid-state imaging device according to claim 11, wherein an end face of the transparent plate is substantially flush with the outer lateral surface of the housing and the end faces of the wiring members.
 13. The solid-state imaging device according to claim 1, wherein the thin portion of the wiring members is exposed from the resin of the base at the side face of the base to permit connecting with an external element as a lateral electrode.
 14. The solid-state imaging device according to claim 1, wherein the lower surface of the thick portion is exposed from the resin of the base at just under the top surface.
 15. A solid-state imaging device, comprising: a base formed with a resin; frame-shaped ribs provided on the base; a plurality of wiring members embedded in the base so as to extend from an internal space of a housing formed by the base and the ribs to an external portion; an imaging element having a photo-detecting portion on a top surface region thereof and fixed to the base inside the internal space; a transparent plate fixed to an upper surface of the ribs; and connecting members electrically connecting electrodes of the imaging element to the wiring members; wherein a plurality of protrusions are provided under a bottom surface of the imaging element, and the imaging element is fixed by an adhesive to the base while being supported from the bottom surface of the imaging element by the protrusions, each of the wiring members has a thin portion and a thick portion, the thin portion is located below the rib so as to be recessed from a lower surface of the thick portion a top surface of the thick portion is connected electrically to the connecting member, a lower surface of the thick portion is exposed from the resin of the base, and a lower surface of the thin portion is covered with the resin of the base.
 16. The solid-state imaging device according to claim 15, wherein the number of protrusions is not less than
 3. 17. The solid-state imaging device according to claim 15, wherein the protrusions are substantially hemispherical.
 18. The solid-state imaging device according to claim 15, wherein the base and the ribs are molded as one piece with a resin with the wiring members embedded.
 19. The solid-state imaging device according to claim 18, wherein the protrusions and the base are formed as one piece with a resin.
 20. The solid-state imaging device according to claim 15, wherein the number of protrusions is not greater than
 5. 21. The solid-state imaging device according to claim 15, wherein the protrusions are made of resin.
 22. The solid-state imaging device according to claim 15, wherein the protrusions are formed in the step of forming the base.
 23. The solid-state imaging device according to claim 15, wherein a thickness at the thick portion of the wiring member is substantially the same as a thickness of the base.
 24. The solid-state imaging device according to claim 15, wherein an outer lateral surface of the housing is substantially flush with end faces of the wiring members.
 25. The solid-state imaging device according to claim 24, wherein an end face of the transparent plate is substantially flush with the outer lateral surface of the housing and the end faces of the wiring members.
 26. The solid-state imaging device according to claim 15, wherein the thin portion of the wiring member is exposed from the resin of the base at the side face of the base to permit connecting with an external element as a lateral electrode.
 27. The solid-state imaging device according to claim 15, wherein the lower surface of the thick portion is exposed from the resin of the base at just under the top surface.
 28. A solid-state imaging device, comprising: a base formed with a resin; frame-shaped ribs provided on the base; a plurality of wiring members embedded in the base so as to extend from an internal space of a housing formed by the base and the ribs to an external portion; an imaging element fixed to the base inside the internal space; a transparent plate fixed to an upper surface of the ribs; and connecting members electrically connecting electrodes of the imaging element to the wiring members; wherein a plurality of protrusions are provided between the base and the imaging element, and the imaging element is fixed by an adhesive to the base while being supported by the protrusions, each of the wiring members has a thin portion and a thick portion, the thin portion is located below the rib so as to be recessed from a lower surface of the thick portion, a top surface of the thick portion is connected electrically to the connecting member, a lower surface of the thick portion is exposed from the resin of the base, and a lower surface of the portion is covered with the resin of the base.
 29. The solid-state imaging device according to claim 28, wherein a material of the protrusion is the same with that of the base.
 30. The solid-state imaging device according to claim 28, wherein the protrusions are formed in a step of forming the base.
 31. The solid-state imaging device according to claim 28, wherein a thickness at the thick portion of the wiring member is substantially the same as a thickness of the base.
 32. The solid-state imaging device according to claim 28, wherein an outer lateral surface of the housing is substantially flush with end faces of the wiring.
 33. The solid-state imaging device according to claim 32, wherein an end face of the transparent plate is substantially flush with the outer lateral surface of the housing and the end faces of the wiring members.
 34. The solid-state imaging device according to claim 28, wherein the thin portion of the wiring member is exposed from the resin of the base at the side face of the base to permit connection with an external element as a lateral electrode.
 35. The solid-state imaging device according to claim 28, wherein the lower surface of the thick portion is exposed from the resin of the base at just under the top surface. 